The present invention relates to a seat structure for a vehicle, which displaces a headrest forward in a rear impact collision.
Japanese Patent Laid-Open No. 10-80338 (see FIGS. 12 to 14) describes a structure, which receives the passenger load in a rear impact collision by moving backward a shock receiving frame 52 located in front of a seatback frame 51, moves the lower end portion of a headrest support frame 53 backward upon backward movement of the shock receiving frame 52, and moves a headrest 55 fixed to the upper end portion of the headrest support frame 53 toward a head 56 of the passenger, since the middle portion of the headrest support frame 53 is axially supported by the seatback frame 51 to be pivotal in the back-and-forth direction.
Japanese Patent Laid-Open No. 7-291005 (see FIGS. 9 to 11) describes a structure in which a coupling member 58, which extends backward upon receiving the passenger load in a rear impact collision, is provided to the coupling portion between a seatback frame 51 that supports a headrest 55, and a cushion member 57 which is provided to the seatback frame 51, the headrest support frame 53 pivots about a pivot member 54 when the coupling member 58 extends backward in a rear impact collision, and the headrest 55 moves forward toward a head 56 of a passenger.
When the upper body of the seated passenger is divided into a lower portion (waist) and an upper portion (chest), and the passenger is normally seated, the lower portion of the upper body contacts a seatback, but the upper portion of the upper body is slightly separated from the seatback. Hence, in a rear impact collision, the seatback receives the load from the lower portion of the upper body, and then that from the upper portion of the upper body. In such rear impact collision, the load from the lower portion of the upper body is larger than that from the upper portion of the upper body. That is, in a rear impact collision, the load from the lower portion (waist) of the upper body is quicker and larger than that from the upper portion of the upper body. Ideally, in a rear impact collision, since the headrest must be quickly and stably moved forward and upward toward the head of a passenger, the present invention is premised on that the headrest is moved forward upon receiving the load from the passenger""s waist, as described in Japanese Patent Laid-Open Nos. 7-291005 and 10-80338 (FIGS. 9 to 14). Under such circumstance, as shown in FIGS. 9 to 14, when the headrest support frame 53 is axially supported by the upper frame of the seatback frame 14, since the spacing between an axial support point 54 of the frame 53 and the shock receiving frame 52 becomes considerably larger than that between the axial support point 54 and headrest 55, it is difficult to assure a required forward moving amount of the headrest. That is, upon displacing the headrest forward by a required amount in a rear impact collision, since the shock receiving frame requires a large moving amount since it receives the passenger""s load, the forward displacement amount of the headrest cannot reach a required level or forward displacement delays. Especially, such problem is conspicuous when the seated passenger is lightweight.
On the other hand, a required forward moving amount of the headrest may be assured by setting the axial support portion of the frame that supports the headrest at substantially the middle position of the seatback in the up-and-down direction, i.e., prolonging the distance from the axial support portion to the headrest. In this structure, since a portion of the frame above the axial support portion is largely displaced forward, the upper portion of the frame may unwantedly push the back of the passenger forward.
The present invention has been made in consideration of the above problems, and has as its object to provide a seat structure for a vehicle, which can quickly and stably move a headrest forward by a required amount upon receiving a load from the passenger""s waist in a rear impact collision.
The present invention has been made in consideration of the above problems, and has as its another object to provide a seat structure for a vehicle, which can suppress forward dislodging of a load transfer portion while quickly and stably moving a headrest forward by a required amount upon receiving a load from the passenger""s waist in a rear impact collision.
In order to solve the aforementioned problems and to achieve the above objects, according to the first invention, since a load transfer portion is axially supported by side surface frames below an upper surface frame, it can receive a load from the passenger""s waist and the headrest can be quickly and stably moved forward by a required amount in a rear impact collision.
According to the second invention, since the instantaneous center of rotation (center of rotation) of the load transfer portion is set above the mean load point (input center) of the load acting from the passenger to a pressure receiving portion and load transfer portion, the headrest can be reliably displaced forward by the load acting from the passenger in a rear impact collision.
According to the third invention, the structure further comprises a first guide for moving the pressure receiving portion backward and upward by the load acting on the pressure receiving portion, and a second guide for moving the load transfer portion upward, the first guide is located below the second guide, and the first and second guides respectively axially support the load transfer portion and pressure receiving portion on the side surface frames below the upper surface frame, thus moving the pressure receiving portion by a simple structure. Also, the headrest can be reliably displaced upward and forward by the backward load acting from the passenger in a rear impact collision.
According to the fourth invention, the first and second guides comprise a combination of link members for coupling the side surface frames and pressure receiving portion, and guide holes which are formed in the side surface frames and guide the load transfer portion upward, thus moving the pressure receiving portion by a mechanically simple structure.
Since the first and second guides have different support structures, even when, for example, a seatback frame has been twisted, the headrest can be stably displaced forward and upward in a rear impact collision. Since one of the first and second guides uses the link member having excellent durability and operation stability, and the other uses the guide hole that can be formed in a small space, operation stability and space savings can be maintained at high level.
According to the fifth invention, since the first guide comprises link members for coupling the side surface frames and pressure receiving portion, and the second guide comprises guide holes which are formed in the side surface frames and guide the load transfer portion upward, the pressure receiving portion can be moved by a mechanically simple structure.
In general, a lumber support that protrudes forward to hold the passenger""s waist is formed on the lower seatback portion, but no lumber support is formed on the upper seatback portion since it disturbs driving operation of the passenger. That is, a member to be disposed inside the seatback can have only a smaller size in the back-and-forth direction of the vehicle body in the upper seatback portion than that in the lower seatback portion, but a structure that does not require any large space, i.e., a guide hole, is adopted for at least the upper axial support point, thus minimizing the member size in the back-and-forth direction of the vehicle body. On the other hand, a guide hole can also be used as the lower axial support point. However the link member has excellent durability and operation stability, and can stably operate by adopting a support method different from that of the upper axial support point even when the seatback frame has been twisted. Furthermore, since the first guide uses the link member which has excellent durability and operation stability, and the second guide uses the guide hole that can be formed in a small space, durability, operation stability, and space savings can be maintained at high level.
According to the sixth invention, since the first guide comprises link members for coupling the side surface frames and pressure receiving portion, and guide holes formed in the side surface frames and guide the load transfer portion upward, and the load from the passenger""s waist is received by the pressure receiving portion, an extra load is input to the first guide in a rear impact collision. Therefore, since the first guide is formed by different mechanisms, i.e., the link member and guide hole, such extra load can be reliably converted into forward displacement of the headrest. Since the link member which has excellent durability and operation stability, and the second guide uses the guide hole that can be formed in a small space are used, durability, operation stability, and space savings can be maintained at high level.
According to the seventh invention, since the guide holes [second guide holes formed in the side surface frames to guide the load transfer portion upward] are formed in an arcuated shape which is convex toward the rear side of the vehicle body, they can move the headrest upward and forward relatively linearly, and can suppress the moving speed of the headrest toward the passenger""s head from considerably changing while the headrest is being displaced at an identical speed.
According to the eighth invention, since the guide hole has a shape that defines the moving path of the headrest to be convex downward compared to a linear path, a high forward moving speed at which the headrest can quickly approach the passenger""s head can be assured.
Also, the distance between the passenger""s head and headrest can be quickly shortened at an early timing of headrest movement, and when the passenger""s head actually contacts the headrest, the relative speed between the passenger""s head and headrest can be minimized (since the moving direction of the headrest has changed in an upward direction). Furthermore, even when the passenger is a child (with a light weight and small height), the headrest can be reliably displaced toward the head of the passenger with a small height at an early timing of movement. When the passenger has a light weight like a child, the headrest cannot often be displaced by a sufficient amount. However, since the forward displacement of the headrest to be preferentially operated by the aforementioned structure is done at an early timing of movement, the headrest can be reliably displaced forward even for a lightweight child.
According to the ninth invention, since the guide hole has a shape that linearly displaces the headrest upward and forward, a nearly constant moving speed of the headrest toward the passenger""s head can be set while the headrest is being displaced at an identical speed.
According to the 10th invention, the load transfer portion crosses the upper surface frame of the seatback on the front side of the vehicle when viewed from the back-and-forth direction of the vehicle body, and allows forward displacement of the headrest, thus quickly displacing the headrest forward.
Since the upper surface frame does not disturb forward movement of the headrest, the headrest can be reliably moved forward in a rear impact collision.
According to the 11th invention, the load transfer portion ordinarily contacts the upper surface frame and can be displaced only toward the front side of the vehicle body to prevent the headrest from moving toward the rear side of the vehicle body, even when the headrest is pressed toward the rear side of the vehicle body or when a portion of the load transfer portion below the axial support points by the side surface frames is pressed. Hence, even when the headrest is pressed from the front side by the head of the seated passenger, or even when the passenger on a rear seat presses the portion of the load transfer portion below the axial support point toward the front side of the vehicle body, the headrest, load transfer portion, and pressure receiving portion can be prevented from being displaced unexpectedly, thus preventing passengers from being disturbed.
According to the 12th invention, the load transfer portion is surrounded by the side surface frames of the seatback to prevent the outer surface shape of the seatback from changing when the headrest has been displaced. Hence, the load transfer portion can move the headrest without disturbing the passenger.
According to the 13th invention, since an allowance portion that allows the passenger""s chest to be displaced backward is formed on the side surface frames above the axial support portions of the load transfer portion, forward dislodging of the load transfer portion can be suppressed while receiving the load from the passenger""s waist, and quickly and stably moving the headrest forward.
According to the 14th invention, since the allowance portion is formed by bending backward a portion of the load transfer portion above the axial support portions, forward dislodging of the load transfer portion can be suppressed by a simple structure.
According to the 15th invention, since at least a portion of the load transfer portion above the axial support portions is comprised of a rectangular frame, and the allowance portion is formed in a space bounded by the rectangular frame, the moving space of the back of the passenger can be assured by a simple structure.
According to the 16th invention, since a shock absorber for absorbing the load that acts upon backward movement of the passenger""s chest is arranged in the space, shock absorbency at the back of the passenger can be improved.
According to the 17th invention, since a restriction member that restricts back-and-forth movement of the headrest support portion is provided to the upper surface frame [upper edge portion of the seatback frame], cluttering of the headrest in an ordinary use can be suppressed.
According to the 18th invention, since the headrest support portion is arranged on the front surface of the upper surface frame [upper edge portion of the seatback frame], and the restriction member restricts forward movement of the headrest support portion, cluttering of the headrest can be suppressed. Also, since the load acting on the headrest in a rear impact collision is received by the seatback frame with high rigidity, the restriction member can have a simple structure.
According to the 19th invention, since the restriction member has a gap that allows movement of the headrest support portion by a predetermined amount, the structure for smoothly moving the headrest forward and upward can be simplified.
According to the 20th invention, since the restriction member is comprised of a lock member that locks a seat surface, its structure can be simple.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.